Blender interface appears gray?
Blender is gray by default:



So it sounds like the theme you were using was somehow reverted.

There is a black theme bundled with blender called Back to Black. If you select it in File menu > User preferences (or CtrlAltU) > Themes > Presets, then blender looks like this:



To set this as your default theme, click Saver user settings at the bottom of the user preferences: